Double dipping / progressive dipping
Double Dipping or Progressive Dipping is a necessary technique in the hot dip galvanizing process used when the object to be coated—such as a very long tube, pipe, or structural member—exceeds the length of the galvanizing kettle.
Technique and Purpose
Since the kettle must contain molten zinc at approximately 450 degrees celsius, its size is physically limited. When a pipe is longer than the kettle, it must be dipped sequentially:
- First Dip: One end of the pipe is fully immersed into the molten zinc up to a designated halfway point or beyond.
- Second Dip: The pipe is removed, the entire kettle is traversed, and the pipe is then immersed from the opposite end until the two coated sections overlap.
This method ensures the entire surface is coated, although the overlapping area receives a slightly thicker layer and may exhibit a noticeable visual transition line. Double dipping is critical for large-scale infrastructure projects, allowing manufacturers to coat components that would otherwise be impossible to handle in standard galvanizing facilities.